This application claims the priority of German Patent Document No. 100 53 361.2, filed in Germany, Oct. 27, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a blade row arrangement for turbo-engines of an axial-flow coaxial construction. Preferred embodiments of the invention relate to a blade row arrangement for turbo-engines, particularly for gas turbines, in an axial-flow coaxial construction with two guide blade rows situated in a fixed axial and circumferential position relative to one another, having a different number of blades and each having a constant pitch angle between their blades, as well as having a moving blade row rotatably arranged between the guide blade rows, the upstream guide blade row having a flow-off direction with an axial and circumferential component comparable with respect to the size.
Promising starting points for optimizing the efficiency of turbo-engines by fluidic measures exist in the form of a fixed defined assignment of the circumferential positions of successive guide blade rows or of successive, synchronously rotating moving blade rows. This principle, which in technical terminology has become known as xe2x80x9cclockingxe2x80x9d or, more concretely, as xe2x80x9cstator or rotor clockingxe2x80x9d, has the object of leading the wakes originating from the individual blades of a first row of blades in a defined fluidically optimal circumferential position to a similar row of blades which is next in the downstream direction. If two xe2x80x9cclockedxe2x80x9d rows of guide blades are involved, it should be taken into account that the wakes are considerably influenced and changed by the moving blade row rotating between the guide blade rows, particularly because of displacements, deformations and separations. The complexity of these flow patterns has the result that so far there are no unambiguous reliable rules for a constructive xe2x80x9cclockingxe2x80x9d.
European Patent Document EP 0 756 667 B1 (corresponding U.S. Pat. No. 5,486,091) protects a xe2x80x9cclockingxe2x80x9d method in which the wakes of a first blade row are directed by a second blade row with a relative motion to the blade inlet edges of a third blade row stationary relative to the first, in which case a maximal circumferential deviation between the wake and the inlet edge of plus/minus 12.5 percent of the blade pitch should be permissible.
Tests have not confirmed that this type of xe2x80x9cclockingxe2x80x9d would generally increase the efficiency.
Irrespective of how the optimal relative circumferential position of the blade rows is selected, it is a prerequisite of xe2x80x9cclockingxe2x80x9d according to the above-mentioned prior art arrangements that the coordinated blade rows pertaining to the same relative system (stator or rotor) have the same number of blades when the blade pitch is circumferentially constant.
It is an object of the invention to suggest a blade row arrangement with two guide blade rows and one moving blade row arranged between the latter which, despite different blade numbers of the two guide blade rows, permits a fluidically advantageous relative circumferential positioning of the guide blade rows in the sense of a xe2x80x9cclockingxe2x80x9d.
This object is achieved in certain preferred embodiments by providing a blade row arrangement for turbo-engines, particularly for gas turbines, in an axial-flow coaxial construction with two guide blade rows situated in a fixed axial and circumferential position relative to one another, having a different number of blades and each having a constant pitch angle between their blades, as well as having a moving blade row rotatably arranged between the guide blade rows, the upstream guide blade row having a flow-off direction with an axial and circumferential component comparable with respect to the size, wherein the blades of the upstream first guide blade row, in one of a first cohesive partial area T1 of the row and a partial area T1 distributed in several separate sectors along the row circumference, successively have an axial offset xcex94m of the same amount as well as in the same direction, wherein the axial offset xcex94m, as a function of the blade number ratio Z1/Z2 of the first and the second guide blade row is selected such that, at Z1 greater than Z2, the axial offset xcex94m increases an effective flow-off cross-section Aeff between the blades, and such that, at Z1 less than Z2 reduces the flow-off cross-section, and wherein the blades of the first guide blade row, in one of a second cohesive partial area T2 of the row and a partial area T2 of the row distributed in several separate sectors along the row circumference, successively have an axial offset xcex94n which has the same size or varies and is oppositely directed in relation to xcex94m.
According to the invention, the upstream guide blade rowxe2x80x94despite a constant pitch angle of the blades along the circumferencexe2x80x94is constructed with two different partial areas which are individually cohesive or distributed in several separate sectors along the row circumference, in both areas each blade being axially offset in a defined manner with respect to its neighboring blade. Thus, the stacking axes of the blades are no longerxe2x80x94as customaryxe2x80x94situated in a common radial plane but on screw surfaces with a constant or varying pitch, in which case concrete blade points are correspondingly situated on helical lines. The first partial area with xcex94m describes, for example, a xe2x80x9cforward screwxe2x80x9d; the second partial area with xcex94n describes a xe2x80x9cbackward screwxe2x80x9d connecting the ends of the xcex94m area, or vice versa. In the sense of a xe2x80x9cclockingxe2x80x9d, only the first partial area acts with a constant defined axial offset xcex94m from blade to blade; the second partial area is used only for the return of the entire added-up axial offset in a linear or non-linear manner by means of xcex94n while avoiding relevant fluidic disadvantages. Since the guide blade rows have a diagonal flow-off with a strong circumferential component, the axial offset between adjacent blades effectively causes an enlargement or reduction of the outlet-side flow cross-section. In the first partial area, the axial offset xcex94m is constant and is selected as a function of the blade number ratio of the two guide blade rows. If the blade number Z2 of the second guide blade row is smaller than that of the first guide blade row (Z1), the effective flow-off cross-section of the first guide blade row is enlarged by means of xcex94m; if Z2 is larger than Z1, the flow-off cross-section of the first row is reduced by means of an opposite axial offset. In the second partial area of the row with the axial offset xcex94n, the opposite will in each case apply correspondingly; here, no targeted xe2x80x9cclocking effectxe2x80x9d occurring at the second downstream guide blade row.
By the variation of the effective flow-off cross-sections of the first guide blade row, the invention results in a certain asymmetry of the flow distribution and thus of the mass distribution in the ring-shaped flow duct cross-section. This has, among others, the advantage that instabilities and disturbances which, in the case of symmetrical or periodic conditions, may expand further over the circumference, can be displaced and partially prevented. Furthermore, by means of the invention, reactions can take place in a targeted manner to certain asymmetries in the afflux.
The xe2x80x9cclocking effectxe2x80x9d primarily endeavored by means of the invention, because of its angular limitation may, for example, also be called xe2x80x9cpartial clockingxe2x80x9d or xe2x80x9csector clockingxe2x80x9d.
Further features of preferred embodiments of the invention are described below and in the claims.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.